The Microtrains GP 9 and 35 would be good starting points for a two truck Nn3 unit.
That thought had occurred to me as well, I have some styrene stock and a bunch of brass doors, vents and details either on hand or on order, and just need to decide if I want to build a four or six axle unit first. If you look around all three MT models GP 9, 35, or SD-40-2, can all be had for around the same price. The F unit is the least expensive though.
